A typical cellular wireless network includes a number of base stations each radiating to define a respective coverage area in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station could be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network could engage in air interface communication with a base station and could thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a cellular wireless network may operate in accordance with a particular air interface protocol or radio access technology, with communications from the base stations to mobile terminals defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include 3G technologies such as Code Division Multiple Access (CDMA) and Global System for Mobile Communication (GSM), 4G technologies such as Long Term Evolution (LTE) (using orthogonal frequency division multiple access (OFDMA) on the downlink and single-carrier frequency division multiple access (SC-FDMA) on the uplink, and developing 5G technologies, among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or range of carrier frequencies. Further, each coverage area may define a number of air interface channels or specific resources for carrying signals and information between the base station and UEs. For instance, certain resources on the downlink may be reserved to carry a reference signal that UEs can measure to evaluate coverage quality, other resources on the downlink may be reserved to carry other control signaling to UEs, and still other resources on the downlink may be reserved to carry bearer traffic and other such communications from the base station to UEs. Likewise, certain resources on the uplink may be reserved to carry various control signaling, such as access requests and scheduling requests, from UEs to the base station, and other resources on the uplink may be reserved to carry bearer traffic and other such communications from UEs to the base station.
When a UE first powers on or otherwise enters into coverage of such a system, the UE may search for a best coverage area in which to operate and may then engage in signaling to acquire wireless connectivity with the base station that provides that coverage area. For instance the UE could search for a coverage area whose downlink reference signal has a highest signal-to-noise ratio (SINR)—as reference signal receive quality (RSRQ)—or a highest signal strength—as reference signal receive power (RSRP). And the UE could then engage in random-access signaling and connection signaling with the base station providing that coverage area, to establish a radio-link-layer connection with the base station. Further, the UE could engage in attach signaling with the network to register for service.
When a UE is served by a base station, the UE may regularly monitor the reference signal from that base station and reference signals from other base stations in the vicinity, to help ensure that the UE continues to operate in a most appropriate coverage area. If the UE finds that one or more other base stations provide sufficiently better coverage than the UE's currently serving base station, then the UE may initiate handover. For instance, the UE may transmit to its serving base station a measurement report that specifies the one or more detected coverage areas and, for each such coverage area, a determined RSRP and/or RSRQ. The serving base station (as source base station) and/or associated network infrastructure may then decide based on the UE's measurement report to coordinate a handover of the UE to a particular base station (as target base station) from which the UE detected best coverage.
Optimally, a wireless service provider will strategically implement base stations throughout a market area so that served UEs can transition between the base stations' coverage areas without experiencing a loss of coverage. Each base station may include an antenna structure and associated equipment, and the service provider may connect each base station by a landline cable (e.g., a T1 line) with the service provider's core network, to enable the base station to communicate on that network.
In some situations, however, it may be impractical for a wireless service provider to run landline connections to base stations. For instance, where a service provider seeks to provide many small coverage areas blanketing a market area or to fill in coverage holes between coverage of other base stations, the service provider may implement many small-cell base stations throughout the market area, but it may be inefficient or undesirable to run landline cables to every one of those small-cell base stations.
To provide coverage in such locations, the wireless service provider may instead implement relays, each of which could be configured to operate in much the same way as a conventional landline-connected base station but could have a wireless backhaul connection to a core network. In particular, each relay could include a relay base station and an associated “UE-relay” module (integrated or communicatively linked together). The UE-relay module, and thus the relay, could then be served by an existing base station of the network, referred to as a donor base station, with the air interface between the UE-relay and the donor base station defining a wireless backhaul connection for the relay. With this arrangement, the relay could thus conveniently communicate with the core network (e.g. with other entities on the core network) via the wireless backhaul connection and the donor base station.